Food pathway and digestive organs
Trace food through the digestive system and state what each organ does.
On this page
Digestion · about 25–35 min
What you need to understand
Food tube: mouth → gullet → stomach → small intestine → large intestine → rectum → anus.
Definitions
- digestion
breaking large insoluble food substances into smaller soluble substances that can be absorbed
For example: Moving food along the gullet is not itself digestion.- absorption
transfer of digested food substances across the gut wall into the body’s transport system
For example: Glucose passes through the small-intestine wall into the blood.- small intestine
the digestive organ where digestion is completed and most nutrients are absorbed
For example: Absorbed nutrients can then be transported to the body’s cells.- large intestine
the digestive organ where water is absorbed from remaining material
For example: It is not the main site of nutrient absorption.- bile
a digestive substance made by the liver and stored in the gall bladder
For example: Bile is released into the small intestine; food does not pass through the liver.
Key idea
- LookTrace food from ingestion to egestion and state the main absorption site.
- ThinkFood tube: mouth → gullet → stomach → small intestine → large intestine → rectum → anus.
- DoTrace food through mouth, gullet, stomach, intestines, rectum and anus while assigning support roles to glands, pancreas, liver and gall bladder.
Explanation
Why food needs to be digested
The body needs nutrients for energy, growth and repair. Large food molecules cannot be absorbed directly. Chemical digestion breaks them into smaller molecules that can cross the gut wall. For example, starch is broken down into small sugars. Once absorbed, nutrients can be transported to cells. Water does not need this breakdown before it can be absorbed.
Chewing breaks food into smaller pieces; enzymes break large food molecules into smaller ones. Both help digestion, but moving food along the tube is a different job.
Follow food through the tube
| Organ | Main function |
|---|---|
| Mouth | Takes in food (ingestion). Teeth chew it, and saliva moistens it and starts chemical digestion. |
| Gullet | Moves swallowed food to the stomach. Waves of muscle contraction push food along; movement does not depend only on gravity. |
| Stomach | Stores food for a time and churns it with digestive juices. Acid provides conditions for stomach enzymes to digest food. |
| Small intestine | Completes digestion and absorbs most nutrients through its wall. For example, absorbed glucose enters the blood. |
| Large intestine | Absorbs water from the remaining material, helping to form faeces. Water is also absorbed in the small intestine. |
| Rectum | Stores faeces before they leave the body. It is the final part of the large intestine. |
| Anus | The opening through which faeces leave the body (egestion). |
Digestive juices join the pathway
Four associated organs supply or store digestive juices. Food does not pass through these organs.
| Associated organ | Main function |
|---|---|
| Salivary glands | Make saliva, which enters the mouth. Saliva moistens food and contains an enzyme that begins digestion. |
| Pancreas | Makes digestive enzymes that enter the small intestine. |
| Liver | Makes bile, which helps fat digestion in the small intestine. |
| Gall bladder | Stores bile and releases it into the small intestine. |
Bile separates large fat droplets into smaller droplets, giving enzymes more surface to act on. Bile is not an enzyme: forming smaller droplets does not itself break fat molecules into smaller molecules.
Keep the processes separate
Digestion breaks down food; absorption moves nutrients across the gut wall into the body; egestion removes undigested and unabsorbed material as faeces. Egestion differs from excretion, which removes wastes made by the body’s cells, such as urea removed by the kidneys.
To compare the pathway map with an anatomical illustration, see the NIDDK explanation of the digestive system
Pause and say it: Food tube: mouth → gullet → stomach → small intestine → large intestine → rectum → anus.
Common mistake
Tempting wrong idea: Digestion makes food substances larger and less soluble.
Why it fails: Nutrients must cross the gut wall, and large food molecules must first be broken down into smaller, absorbable substances. Digestion therefore breaks large, insoluble food substances into smaller, soluble ones.
Use this instead: Digestion breaks large food substances into smaller soluble products that can be absorbed.
Practical work
What to show: Trace food through mouth, gullet, stomach, intestines, rectum and anus while assigning support roles to glands, pancreas, liver and gall bladder.
Before you finish: Movement and digestion can occur in the same system but are different processes.
Practical link: The topic investigation is taught in “Enzymes and rate data”
6. Worked Examples
Modelled example 1
Trace a meal
Problem
Trace food from ingestion to egestion and state the main absorption site.
Study the worked solution
Reason from the evidence
Method
Order the organs food passes through and mark where digested nutrients cross the gut wall into the body.
Reason
The route through the food tube is different from the route taken by absorbed nutrients and from the roles of associated organs.
Working
Food enters the mouth, passes through gullet and stomach, then small intestine.
Most digested nutrients are absorbed through the small intestine.
The large intestine absorbs water from the remaining material. The rectum stores faeces before they leave through the anus.
State the conclusion
Working
The food tube has a sequence; liver, pancreas and gall bladder support digestion but food does not pass through them.
Common misconception 2
Movement is not the same as digestion
Learner response
“Food is digested when it moves down the gullet, then egested when nutrients enter the blood.” Correct both parts.
Use digestion, absorption and egestion accurately
View solution step by step
Separate three processes
Method
Name what changes food, what moves nutrients into the body and what removes undigested material.
Reason
These processes occur for different reasons and at different parts of the system.
Working
Movement down the gullet transports food but is not itself digestion. Digestion breaks large food molecules into smaller soluble molecules. Absorption moves digested nutrients through the small-intestine wall into the body’s transport system; glucose, for example, enters the blood. Egestion removes undigested material through the anus.
Challenge 3
Predict the effect of poor absorption
Problem
A condition damages the lining of the small intestine, so it cannot absorb nutrients normally. Food is still broken down normally. Predict the most direct effect on the person’s nutrition and explain your reasoning.
Follow the nutrients from digestion to the body
Hints
Hint 1: site
What normally passes through the small-intestine wall?
Hint 2: destination
Where should digested nutrients go next?
View solution step by step
Link organ to function
Method
Focus on absorption because digestion is stated to be normal.
Reason
Digested nutrients must cross the small-intestine wall before the body can transport and use them.
Working
Poor absorption means fewer digested nutrients enter the body even though digestion has occurred. The person could therefore obtain less usable nutrition from the same food.
Guided practice
Try it with support
Trace food from mouth to anus, then state the roles of the pancreas, liver and gall bladder without placing them in the food tube.
Use the pathway in order.
Name the digestive enzymes from the pancreas and trace bile from its source.
Check the guided answer
Answer: Food passes mouth → gullet → stomach → small intestine → large intestine → rectum → anus. The pancreas supplies digestive enzymes to the small intestine, the liver makes bile and the gall bladder stores and releases bile.
Check: Most nutrient absorption occurs in the small intestine; the large intestine absorbs water from the remaining material.
Practise and continue
Practise this
Explain why movement through the gullet is not by itself digestion.
Need a hint?
Use large, insoluble and small, soluble in the definition.
Check your answer
Answer: The gullet transports food. Digestion requires large insoluble food substances to be broken into smaller soluble substances that can be absorbed.
Check: Movement and digestion can occur in the same system but are different processes.
Think like a scientist
Why is a digestive-system diagram a model rather than a scale picture?
Check the reasoning
It preserves organ order and connections but simplifies three-dimensional shape, relative size, movement and internal tissue structure.
Remember: Use the model for pathway reasoning, not for exact anatomical scale.
One-minute check
Hide the page and trace food from the mouth to the anus. Where are most nutrients absorbed?
Where is bile made and stored, and where does it act?
Correct this common mistake: “Digestion makes food substances larger and less soluble.”
Syllabus and review details
- SEC G1 Science 2027 · 2027
Content structure and syllabus content, PDF pages 8–17
Last reviewed: